Tunable Laser

Abstract

A tunable laser comprising a first wafer, a second wafer, and an optical cavity. The first wafer is made of a first semiconductor material. The first wafer supports an optical amplifier and an electro-optically tunable optical filter. The second wafer is made of a second material different from the first semiconductor material. The second wafer supports a thermally tunable optical filter. The optical cavity includes the optical amplifier, the electro-optically tunable optical filter, and the thermally tunable optical filter.

Description

[Background technology]

[0001] Tunable lasers are used to generate light of at least one of tunable wavelength and tunable power. Adjustment of the wavelength and / or power output by a tunable laser can be for communications and / or optical systems. It would be desirable to provide an improved tunable laser. [Brief explanation of the drawings]

[0002] [Figure 1] 1 shows a schematic plan view of a tunable laser according to an embodiment; [Figure 2] 1 shows a schematic plan view of a tunable laser according to an embodiment; [Figure 3] 1 shows a schematic plan view of a tunable laser according to an embodiment; [Figure 4] 1 shows a schematic plan view of a tunable laser according to an embodiment; [Figure 5] 1A and 1B show schematic diagrams of plan views of parts of a photonic integrated circuit (PIC) according to an embodiment; [Figure 6] 1 shows a schematic plan view of a device according to an embodiment; [Figure 7] 1 illustrates a method for fabricating a tunable laser according to an embodiment; [Figure 8] 1 illustrates a method for fabricating a tunable laser according to an embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0003] In a described embodiment, the tunable laser includes a first wafer of a first semiconductor material. The first wafer supports an optical amplifier and an electro-optically tunable optical filter. The tunable laser further includes a second wafer of a second material different from the first semiconductor material. The second wafer supports a thermally tunable optical filter. The tunable laser comprises an optical cavity including the optical amplifier, the electro-optically tunable optical filter, and the thermally tunable optical filter. The combination of the electro-optically tunable optical filter and the thermally tunable optical filter is configured to adjust at least one of the power or wavelength of light output by the tunable laser. In doing so, the tunable laser can provide, for example, an output of a selected wavelength and / or power. The output of the tunable laser is for use in photonic devices or systems, such as for medical imaging, spectroscopy, telecommunications, optical data transmission, random number generation, and light detection and ranging (LIDAR).

[0004] At least one of the electro-optically tunable optical filter or the thermally tunable optical filter may be configured to suppress undesired wavelengths of light, such that the output of the tunable laser is switchable between different wavelengths. Spectral filtering of the output of the tunable laser is desirable for applications such as communications, spectroscopy, or imaging, for example. This may reduce the need for additional optical components for wavelength tuning, which may simplify the manufacture of devices including the tunable laser, reduce the footprint of devices including the laser, and / or reduce the cost of manufacturing devices including the laser.

[0005] At least one of the electro-optically tunable optical filter or the thermally tunable optical filter may be configured to modulate the power of the output of the tunable laser, and in such embodiments, the electrical signal may be directly converted to an optical signal. In some embodiments, modulating the power of the output of the tunable laser in response to an electrical signal input to the electrically tunable optical filter may be desirable for applications such as communications. This may reduce the need for additional optical components for electro-optic modulation, which may, for example, simplify the manufacture of devices including the tunable laser, reduce the footprint of devices including the laser, and / or reduce the cost of manufacturing devices including the laser.

[0006] In some embodiments, the output of the tunable laser has a single wavelength intensity peak that is tunable over a range, for example, within a range of 10 nanometers to 1 millimeter. The single intensity peak tuning and / or wavelength tuning can be achieved by superposition of a thermally tunable optical filter and an electro-optically tunable optical filter. In some embodiments, the light amplified by the optical amplifier is for amplifying infrared light, and in some such embodiments, the wavelength of the output of the tunable laser is tunable between 1530 nanometers and 1565 nanometers. Such wavelengths can be used in telecommunications applications.

[0007] A tunable optical filter is an optical element that can be adjusted to adjust its output spectrum (e.g., output frequency spectrum). A tunable optical filter may include at least one of a tunable resonator or an interferometer.

[0008] An electro-optically tunable optical filter is a tunable optical filter. The output spectrum of an electro-optically tunable filter is tunable by electro-optic effects such as the Pockels effect or the Kerr effect, in which the refractive index of a material depends on an electric field applied to it. An electro-optically tunable optical filter may be a diode and / or may be reverse-biased. Therefore, electro-optically tunable optical filters require materials that exhibit the electro-optic effect, such as indium phosphide (InP), indium gallium arsenide phosphide (InGaAsP), aluminum gallium arsenide (AlGaAs), lithium niobate (LiNbO), and beta-barium borate (BBO).

[0009] A thermally tunable optical filter is a tunable optical filter. The output spectrum of a thermally tunable optical filter can be tuned by the thermo-optic effect. The thermo-optic effect causes the refractive index of a material to depend on the temperature of the material. Therefore, thermally tunable optical filters require materials that exhibit the thermo-optic effect and are mechanically resilient to temperature changes, such as silicon (Si) or silicon nitride (SiN).

[0010] The first semiconductor material is different from the second material. In some such embodiments, the first semiconductor material exhibits an electro-optic effect and the second material exhibits a thermo-optic effect. The use of such materials may increase design freedom within the tunable laser, and in some such embodiments, the tunable laser includes an electro-optic component, a thermo-optic component, an electro-optically tunable optical filter, and a thermally tunable optical filter. It has been found desirable to use a material, such as a material having an electro-optic effect, for the electro-optically tunable optical filter and a different material, such as a material having a thermo-optic effect, for the thermally tunable optical filter. In some embodiments, the first semiconductor material is InP and the second material is SiN. It should be noted that the first semiconductor material may also exhibit, to some extent, a thermo-optic effect in some embodiments, and / or the second material may also exhibit, to some extent, an electro-optic effect, although the tunable lasers in embodiments herein are configured not to utilize these effects for tuning. Instead, the laser is configured to use the electro-optic effect of the first semiconductor material and the thermo-optic effect of the second material.

[0011] Terms and features used herein, such as waveguides, tunable resonators, and interferometers, will be explained in more detail below. However, it is useful here to explain in more detail the wafers referred to herein. A wafer may also be referred to as a chip, slice, substrate, or layer. A wafer is, for example, a generally flat or relatively thin piece of material, and in some embodiments, is crystalline. A wafer may be a disk or portion of a disk of crystalline Si used in semiconductor foundries, and in some such embodiments, a 125 gram, 300 millimeter diameter disk. Alternatively, a wafer may be a disk or portion of a disk of crystalline InP used in semiconductor foundries, and in some such embodiments, a 25 millimeter, 51 millimeter, 76 millimeter, 100 millimeter, 200 millimeter, or 300 millimeter diameter disk.

[0012] A general introduction to embodiments of the present specification relating to tunable lasers will now be provided with reference to FIG. 1. FIG. 1 schematically illustrates a plan view of a tunable laser 100. The tunable laser 100 includes a first wafer 102 of a first semiconductor material. The first wafer 102 supports or includes an optical amplifier 104 and an electro-optically tunable optical filter 106. The tunable laser 100 further includes a second wafer 110 of a second material. The second material is different from the first semiconductor material. The second wafer 110 supports or includes a thermally tunable optical filter 108. The second wafer 110 is optically connected to the first wafer 102. The tunable laser 100 includes an optical cavity 120. The optical cavity includes the optical amplifier 104, the electro-optically tunable optical filter 106, and the thermally tunable optical filter 108. Other arrangements of elements configured as an optical cavity according to the illustrated arrangement are also envisioned. The first wafer 102 is in contact with and abuts the second wafer 110. In other embodiments not shown, the first wafer is optically connected to the second wafer and is not in contact with the second wafer. In various embodiments, the first wafer is on top of the second wafer, the second wafer is on top of the first wafer, the first wafer supports the second wafer, and / or the second wafer supports the first wafer. In FIG. 1, dashed lines are used to indicate where the first wafer or second wafer may extend laterally beyond the illustration (e.g., as part of a PIC).

[0013] Further embodiments of the present specification relating to tunable lasers will now be described with reference to Figure 2. In some embodiments, the optical cavity is configured as a ring optical cavity, e.g., components within the cavity are optically connected in series to form a ring. Such tunable lasers are sometimes referred to as tunable ring lasers. Tunable ring lasers can be used in ring laser gyroscopes or devices for gravitational waves, relativistic effects, or quantum electrodynamic effects.

[0014] Figure 2 schematically illustrates a plan view of a tunable laser 200 according to an embodiment described herein. Where features relating to Figure 2 correspond to features described using Figure 1, reference numbers that are 100 higher than the corresponding reference numbers used in Figure 1 are used (e.g., 102 in Figure 1 is 202 in Figure 2), and the corresponding description for such features also applies here. As in Figure 1, dashed lines are used to indicate where the first wafer or second wafer may extend laterally beyond the figure (e.g., as part of a PIC).

[0015] Optical cavity 220 is configured as a ring optical cavity 220, although ring optical cavity configurations other than that shown are contemplated. Tunable laser 200 includes a first wafer 202 that supports and / or comprises an optical amplifier 204 optically connected to an electro-optically tunable optical filter 206 by a first waveguide 215. Tunable laser 200 further includes a second wafer 210 that supports and / or comprises a thermally tunable optical filter 208 optically connected to optical amplifier 204 by a second waveguide 213. Second wafer 210 is optically connected to first wafer 202 by second waveguide 213. Thermally tunable optical filter 208 is optically connected to electro-optically tunable optical filter 206 by a third waveguide 211 to form ring optical cavity 220. Ring optical cavity 220 includes optical amplifier 204, electro-optically tunable optical filter 206, and thermally tunable optical filter 208. Other arrangements of elements configured as a ring optical cavity according to the illustrated arrangement are also envisioned.

[0016] Further embodiments herein relating to tunable lasers will now be described with reference to FIG. 3 . In some embodiments, the optical cavity is a linear optical cavity. Components within the linear optical cavity are optically connected in series with reflectors, partial reflectors, resonators, and / or interferometers at each end of the linear optical cavity. Such tunable lasers are sometimes referred to as tunable linear lasers or linear tunable lasers. For example, linear optical cavities reduce the footprint of linear tunable lasers and / or achieve more efficient filtering of lasing modes compared to other cavity configurations, such as ring cavities.

[0017] While Figure 3 schematically illustrates a plan view of an example tunable laser 300 described herein, in which the optical cavity 320 is configured as a linear optical cavity 320, configurations of the optical cavity other than that shown are contemplated. Other arrangements of elements configured as an optical cavity according to the arrangement shown are also contemplated. Where features relating to Figure 3 correspond to features described using Figure 1, reference numbers 200 higher than the corresponding reference numbers used in Figure 1 are used (e.g., 102 in Figure 1 is 302 in Figure 3), and the corresponding descriptions for such features also apply here. As with Figures 1 and 2, dashed lines are used to indicate where the first wafer or second wafer may extend laterally beyond the figure (e.g., as part of a PIC).

[0018] The tunable laser 300 includes a first wafer 302 that supports and / or comprises an optical amplifier 304 optically connected to an electro-optically tunable optical filter 306 by a second waveguide 316. The first wafer 302 also supports and / or comprises a resonator 312. In other embodiments, the resonator is at least one of a reflector, a partial reflector, or an interferometer. The resonator 312 is optically connected to the optical amplifier 304 by a fourth waveguide 324. The tunable laser 300 further includes a second wafer 310 that supports and / or comprises a thermally tunable optical filter 308 optically connected to the electro-optically tunable optical filter 306 by a first waveguide 314. The second wafer 310 is optically connected to the first wafer 302 by the first waveguide 314. The second wafer 302 also supports and / or comprises a multi-mode interferometer (MMI) 318. In other embodiments, the MMI 318 is at least one of a reflector, a partial reflector, a resonator, or another configuration of an interferometer. The MMI 318 is optically connected to the thermally tunable optical filter 308 by a third waveguide 326. The MMI 318 has an output 322 that is the output of the tunable laser 300. The linear optical cavity 320 comprises the resonator 312, the optical amplifier 304, the electro-optically tunable optical filter 306, the thermally tunable optical filter 308, and the MMI 318.

[0019] Further embodiments of the present specification relating to tunable lasers will now be described with reference to FIG. 4. FIG. 4 schematically illustrates a plan view of a tunable laser 400 according to embodiments described herein. Where features relating to FIG. 4 correspond to features described using FIG. 3, reference numerals 100 higher than the corresponding reference numerals used in FIG. 3 are used (e.g., 302 in FIG. 3 is 402 in FIG. 4), and the corresponding descriptions for such features also apply here. As with FIGS. 1-3, dashed lines are used to indicate where a second wafer may extend laterally beyond the figure (e.g., as part of a PIC). A first wafer 402 is supported by and rests on a second wafer 410. In other embodiments not shown, the second wafer is supported by and / or rests on the first wafer. The tunable laser 400 includes a first wafer 402 supporting and / or comprising an optical amplifier 404 optically connected to an electro-optically tunable optical filter 406 by a second waveguide 416. The electro-optically tunable optical filter 406 includes tunable ring resonators 428 and 430. The tunable ring resonators 428 and 430 of the electro-optically tunable optical filter 406 are optically connected by at least one MMI and / or at least one waveguide. In another embodiment not shown, the electro-optically tunable optical filter includes an interferometer. The tunable laser 400 further includes a second wafer 410 supporting and / or comprising a thermally tunable optical filter 408 optically connected to the electro-optically tunable optical filter 406 by a first waveguide 414. The thermally tunable optical filter 408 includes a tunable ring resonator 432 and an interferometer 434. In other embodiments not shown, the thermally tunable optical filter includes a plurality of tunable ring resonators. The tunable ring resonators 432 are optically connected to the interferometer 434 by at least one MMI and / or at least one waveguide. In various embodiments, at least one of the electro-optically tunable optical filter or the thermally tunable optical filter comprises a tunable resonator.The second wafer 402 supports and / or contains a first MMI 418 and a second MMI 436. The MMI 418 is optically connected to the thermally tunable optical filter 408 by a third waveguide 426. The second MMI 436 is optically connected to the optical amplifier 404 by the third waveguide 426. The first MMI 418 has an output 422, which is the output of the tunable laser 400. The second wafer 410 is optically connected to the first wafer 402 by a first waveguide 414 and a fourth waveguide 425. The tunable laser 400 comprises an optical cavity comprising the optical amplifier 404, the electro-optically tunable optical filter 406, the thermally tunable optical filter 408, the first MMI 418, and the second MMI 436.

[0020] Next, with reference to FIG. 5 , embodiments herein related to PICs will be described. The tunable laser may be configured for use within or integrated into a generic photonic platform. In some embodiments, at least one of the first wafer or the second wafer is a substrate for the PIC, and in other embodiments, the first wafer and the second wafer are supported by and / or on the substrate for the PIC. The generic photonic platform uses standardized processes for fabricating photonic components and / or standardized photonic components for the resulting PIC. Integration into a generic photonic platform may simplify the combination of the tunable laser with one or more components of the PIC. The tunable laser may be integrated into the generic platform. In some such embodiments, PICs are easier, cheaper, and faster to fabricate and have a wide range of applications. The PIC integrates multiple photonic functions, such as lasers or photodiodes, although other photonic functions are also envisioned. In an embodiment shown schematically and in plan view by Figure 5, a photonic integrated circuit 540 comprises a tunable laser 500 according to an embodiment described herein. Where features relating to Figure 5 correspond to features described using Figure 1, reference numerals are used that are 400 higher than the corresponding reference numerals used in Figure 1 (e.g., 102 in Figure 1 is 502 in Figure 5), and the corresponding description for such features also applies here.

[0021] The PIC 540 includes a tunable laser 500 supported by and on a substrate 538. The first wafer 502 and second wafer 510 of the tunable laser 500 are on the substrate 538, which is for the PIC 540. In other embodiments not shown, the substrate is not for a PIC, but is, for example, a printed circuit board (PCB), an integrated circuit (IC), or a support for the tunable laser 500. The support for the tunable laser may increase the thermal and / or mechanical stability of the laser, thereby improving the performance of the tunable laser. In some embodiments, the tunable laser is integrated into the PIC. Dashed lines are used to indicate that in some embodiments, either the first wafer or the second wafer is part of the substrate. In some embodiments, the substrate is made of a third material, and in some such embodiments, either the first semiconductor material or the second material is the same as the third material.

[0022] Next, embodiments of the present specification relating to devices will be described with reference to FIG. 6. Some embodiments of the present specification relate to devices including a PIC as described herein. FIG. 6 schematically illustrates a plan view of at least a portion of a photonic device 642 including a PIC 640 having a tunable laser 600. Where features relating to FIG. 6 correspond to features described using FIG. 3 or FIG. 5, reference numerals are used that are 300 or 100 higher than the corresponding reference numerals used in FIG. 3 or FIG. 5, respectively (e.g., 302 in FIG. 3 is 602 in FIG. 6, and 538 in FIG. 5 is 638 in FIG. 6), and the corresponding descriptions for such features also apply here.

[0023] The optical device 642 includes an output of light 622, for example, for light emission applications such as LIDAR. In other embodiments not shown, the photonic device does not emit light. For example, in the case of a random number generator photonic device, little or no light emitted within the PIC leaves the PIC. The photonic device includes a controller 646 electrically connected to the tunable laser 600 by an electrical connection 648. In some embodiments, the controller 630 is for modulating the power of the output 622 of the tunable laser 600 or for modulating the peak wavelength of the output 622. The controller 646 can be a control circuit, an IC, a processor, a microcontroller, or a computer. Other controllers are also contemplated. In some embodiments, the PIC 640 includes electrical circuitry and / or components of the PIC 640 are externally controlled by appropriate electrical connections to electrodes or other electrical contacts on the PIC 640.

[0024] Referring now to FIGS. 7 and 1, an example method 750 for fabricating a tunable laser 100 according to an embodiment described herein (such as the embodiment of FIG. 1) will be described. (Although FIG. 1 is used as an example, method 750 is also applicable to any of the embodiments of FIGS. 2-4.) FIG. 7 schematically illustrates method 750 including providing 752 a first wafer 102 of a first semiconductor material. The first wafer 102 supports an optical amplifier 104 and an electro-optically tunable optical filter 106. Providing 752 the first wafer 102 may include using a pre-assembled wafer, a pre-formed wafer, and / or a pre-processed wafer. In other embodiments, providing 752 the first wafer includes assembling, processing, and / or forming the first wafer 102. The method then includes providing 754 a second wafer 110 of a second material different from the first semiconductor material. The second wafer 110 supports a thermally tunable optical filter 108. Providing 754 the second wafer 110 may include using a pre-assembled wafer, a pre-formed wafer, and / or a pre-processed wafer. In other embodiments, providing 754 the second wafer includes assembling, processing, and / or forming the first wafer. Next, the method includes optically coupling 756 the first wafer 102 to the second wafer 110 such that the optical cavity 120 of the tunable laser 110 comprises the optical amplifier 104, the electro-optically tunable optical filter 106, and the thermally tunable optical filter 108. Such a method may be referred to as hybrid integration. The first and second wafers may be optically coupled by mechanically connecting the first and second wafers 102 and 104. In other embodiments, the first and second wafers are optically coupled and are not mechanically coupled and / or in contact. Mechanically connecting the first wafer 102 and the second wafer 110 may include directly or indirectly bonding and / or attaching the first wafer 102 to the second wafer 110.In other embodiments, mechanically connecting the first wafer 102 to the second wafer 110 includes attaching and / or bonding both the first wafer 102 and the second wafer 110 to a substrate, or in other embodiments, microtransfer printing the first wafer onto the second wafer, or microtransfer printing at least one of the first wafer or the second wafer onto a substrate. In further embodiments, mechanically connecting the first wafer 102 and the second wafer 110 includes abutting the first wafer 102 and the second wafer 110. Other mechanical connections between the first wafer 102 and the second wafer 110 are also contemplated. Hybrid integration refers, for example, to when the tunable laser 100, PIC, or photonic device is fabricated by providing a first wafer 102 supporting photonic components and a second wafer 110 supporting photonic components, and then optically connecting the first wafer 102 and the second wafer to each other. Hybrid integration may include processes and / or techniques for providing a first wafer 102 or photonic components supported by the first wafer 102 that are incompatible with a second wafer 110 or photonic components supported by the second wafer. Hybrid integration may include processes and / or techniques for providing a second wafer 110 or photonic components supported by the second wafer 110 that are incompatible with a first wafer 102 or photonic components supported by the first wafer 102. In some embodiments of hybrid integration, providing 752 the first wafer 102 supporting the optical amplifier 104 and the electro-optically tunable optical filter 106 and providing 754 the second wafer 110 supporting the thermally tunable optical filter 108 are performed at different times, by different parties, or at different geographic locations. Some embodiments herein relate to methods of fabricating a PIC, including a method 750 of fabricating a tunable laser 100 described herein.Additionally, some embodiments herein relate to methods of manufacturing devices, including a method 750 of manufacturing a tunable laser 100 described herein or a method of manufacturing a PIC described herein.

[0025] Referring now to FIG. 8 and FIG. 1, a further example of a method 860 for fabricating a tunable laser 100 according to embodiments described herein (such as the embodiment of FIG. 1) will be described. (Although FIG. 1 is used as an example, the method 750 is also applicable to any of the embodiments of FIGS. 2-4.) FIG. 8 schematically illustrates the method 860 including providing 862 a first wafer 102 of a first semiconductor material. Providing 862 the first wafer 102 may include using a pre-assembled wafer, a pre-formed wafer, and / or a pre-processed wafer. In other embodiments, providing 862 the first wafer 102 may include assembling, processing, and / or forming the first wafer 102. Next, the method includes providing 864 a second wafer 110 of a second material. Providing 864 the second wafer 110 may include using a pre-assembled wafer, a pre-formed wafer, and / or a pre-processed wafer. In other embodiments, providing 864 the second wafer 110 includes assembling, processing, and / or forming the second wafer 110. Next, the method includes mechanically connecting 866 the first wafer 102 to the second wafer 110. Similar to that described with respect to FIG. 7 , mechanically connecting the first wafer 102 and the second wafer 110 can include directly bonding and / or attaching the first wafer 102 to the second wafer 110. In other embodiments, mechanically connecting the first wafer 102 to the second wafer 110 includes attaching and / or bonding both the first wafer 102 and the second wafer 110 to a substrate. In further embodiments, mechanically connecting the first wafer 102 and the second wafer 110 includes abutting the first wafer 102 and the second wafer 110. Other mechanical connections between the first wafer 102 and the second wafer 110 are also contemplated.Next, the method includes forming 868 the electro-optically tunable optical filter 106 and the optical amplifier 104 on the first wafer 102 and the thermally tunable optical filter 108 on the second wafer 110, such that the optical cavity 120 of the tunable laser 100 includes the optical amplifier 104, the electro-optically tunable optical filter 104, and the thermally tunable optical filter 108. The optical cavity 120 may be constructed by optically connecting the first wafer 102 and the second wafer 110 to each other. Heterogeneous integration is when the tunable laser 100, PIC, or photonic device is fabricated, for example, by using processes and / or techniques that mechanically connect the first wafer 102 and the second wafer 110 and then provide the desired photonic components supported by the first wafer 102 and / or the second wafer 110. Heterogeneous integration may include using a single die and / or a generic platform to provide the tunable laser 110, the PIC, or the photonic device. Heterogeneous integration may reduce the foundry time required to fabricate the tunable laser and / or the footprint of the tunable laser 100. Some embodiments herein relate to methods of fabricating a PIC, including the method 860 of fabricating the tunable laser 100 described herein. Additionally, some embodiments herein relate to methods of fabricating a device, including the method 860 of fabricating the tunable laser 100 described herein or the method of fabricating the PIC described herein.

[0026] Example methods described herein can include providing a controller as described above, where the controller is configured, for example, for at least one of modulating the power of an output of the tunable laser or modulating a peak wavelength of the output.

[0027] As those skilled in the art will appreciate, the first wafer, the second wafer, or one or more of the components of the tunable laser can be provided by being formed during the manufacturing process using known techniques, such as, for example, metalorganic vapor phase epitaxy (MOVPE), surface passivation, photolithography, ion implantation, etching, dry etching, ion etching, wet etching, buffered oxide etching, plasma ashing, plasma ashing, heat treatment, annealing, thermal oxidation, chemical vapor deposition, atomic layer deposition, physical vapor deposition, molecular beam epitaxy, laser lift-off, electrochemical deposition, electroplating, or chemical-mechanical polishing. In some embodiments, as those skilled in the art will appreciate, etching techniques are used to remove portions of material as part of patterning. Those skilled in the art will appreciate that the first wafer and the second wafer can be mechanically and / or optically connected using known techniques, such as wafer fusing, anodic bonding, adhesive bonding, etc. Those skilled in the art will readily appreciate how to form an optical amplifier, an electro-optically tunable optical filter, or a thermally tunable optical filter on the surface of the wafer.

[0028] An explanation of some of the terms and features used above will now be provided to further explain the features of the embodiments described herein.

[0029] The waveguide herein is for guiding light. Light propagates within the waveguide and is confined within the waveguide due to reflections at the waveguide's boundaries. The waveguide has a refractive index greater than the refractive index of the material in contact with the waveguide at the boundary where it is desired to guide the light. In this manner, the waveguide guides the propagation of light. For light to propagate within the waveguide, it is desirable for the light reflected at the waveguide's boundary to satisfy the condition for constructive interference. In some embodiments, the waveguide is at least one of a semiconductor junction or an electrorefractive modulator.

[0030] Optical amplifiers are used to increase the power of a tunable laser's output by amplifying light within an optical cavity. In some embodiments, the light emitted from the tunable laser is both spatially and temporally coherent. In some embodiments, optical amplification is achieved by at least one of stimulated emission and spontaneous emission due to electron-hole recombination. The wavelength of the light amplified by the optical amplifier can be between 10 nanometers and 1 millimeter. Examples of optical amplifiers include solid-state amplifiers, doped fiber amplifiers, semiconductor amplifiers, Raman amplifiers, or parametric amplifiers. The optical amplifier can include InGaAsP or aluminum indium gallium arsenide (AlInGaAs). Other optical amplifiers are also contemplated. The optical amplifier can include an alloy of a first semiconductor material, e.g., the optical amplifier includes InGaAsP and the first semiconductor material is InP. This can simplify incorporating the optical amplifier into a first wafer of a tunable laser, providing the first wafer including the optical amplifier, and / or forming the optical amplifier on the first wafer.

[0031] A resonator, a reflector, a partial reflector, or an interferometer may be used to provide at least one end of the optical cavity. The reflector may be a mirror. The resonator may be a ring resonator. The interferometer may be an MMI. In some examples, the resonator comprises a ring along the circumference of which light propagates, and the circumference of the ring is such that a standing wave is generated when light is injected into the resonator. Other tunable resonators are contemplated, such as a planar-parallel resonator, a concentric resonator, a confocal resonator, a disk resonator, a toroidal resonator, or a hemispherical resonator.

[0032] A tunable resonator is a structure configured so that optical modes within the tunable resonator interfere to cause constructive or destructive interference, depending on the effective path length or lengths within the structure and / or the wavelength of the mode or modes. In some embodiments, the tunable resonator is a tunable ring resonator and includes a ring waveguide structure. The tunable ring resonator may include two waveguides, one end of which is optically coupled to a first power coupler and the other end of which is optically coupled to a second power coupler (e.g., an MMI) to form a ring. The radius of the tunable ring resonator may be selected, for example, for mode selection. The waveguides of the tunable ring resonator may be curved to form a ring, and in some such embodiments, the tunable ring resonator is not circular. Adjusting the optical path length or refractive index within the resonator tunes the wavelength of the tunable resonator's output spectrum.

[0033] Interferometers are used to interfere with multiple optical modes. A phase difference between the optical modes results in constructive or destructive interference. In some embodiments, the interferometer is a Mach-Zehnder interferometer (MZI), such as an asymmetric MZI (AMZI). Other exemplary interferometers are a Fizeau interferometer, a Fabry-Perot interferometer, a Michelson interferometer, or a Lyot interferometer, although other interferometers are also contemplated. The phase difference between the optical modes can be adjusted by adjusting the optical path length or refractive index within the interferometer, which adjusts the wavelength of constructive or destructive interference within the interferometer, thereby adjusting the output spectrum and / or power of the interferometer.

[0034] The free spectral range of a tunable optical filter is the wavelength separation between two consecutive reflected or transmitted power maxima of the tunable optical filter. In some embodiments, the free spectral range of the electro-optically tunable optical filter is different from the free spectral range of the thermally tunable optical filter, while in other embodiments, the free spectral range of the electro-optically tunable optical filter is the same as the free spectral range of the thermally tunable optical filter. In some embodiments where there is a difference between the free spectral range of the electro-optically tunable optical filter and the free spectral range of the thermally tunable optical filter, the linewidth of the output of the tunable laser may be narrow. Linewidth, as used herein, refers to the full width at half maximum (FWHM) of the peak of the output spectrum of the tunable laser. The linewidth may be, for example, at least one of less than 100 kilohertz, less than 50 kilohertz, less than 20 kilohertz, less than 10 kilohertz, or less than 2 kilohertz.

[0035] The scanning speed of the tunable optical filter is the maximum speed at which the peak transmission wavelength of the tunable optical filter can be tuned, e.g., in nanometers per second. In some embodiments, the scanning speed of the electro-optically tunable optical filter is different from the scanning speed of the thermally tunable optical filter, and in other embodiments, the scanning speed of the electro-optically tunable optical filter is the same as the scanning speed of the thermally tunable optical filter. In some embodiments, the electro-optically tunable optical filter is for modulating the wavelength of the output of a tunable laser. For example, the scanning speed of the electro-optically tunable optical filter can be faster than the scanning speed of the thermo-optically tunable optical filter because electro-optic tuning requires less heat dissipation than thermo-optic tuning. Faster scanning speeds of electro-optically tunable optical filters are for, e.g., imaging or telecommunications applications. In some embodiments, the scanning speed of the electro-optically tunable optical filter is at least 100 times, 1000 times, 10,000 times, 100,000 times, or 1,000,000 times faster than the scanning speed of the thermally tunable optical filter. Electro-optical regulation may require less power consumption than thermo-optical regulation, for example in low power devices or applications.

[0036] The low-resonance FWHM may be provided by a thermally tunable optical filter, and / or the high-speed modulation may be provided by an electro-optically tunable optical filter. The optical cavity is an arrangement of optical elements as a cavity resonator for forming a standing light wave. The optical cavity may be provided by optically connecting an optical amplifier, an electro-optically tunable optical filter, and a thermally tunable optical filter. The optical cavity includes an optical amplifier, an electro-optically tunable optical filter, and a thermally tunable optical filter.

[0037] Optically coupled refers to, for example, optically coupled optical elements configured to allow light to propagate through free space between the optically coupled optical elements, and / or optically coupled optical elements optically connected by a waveguide, configured to allow light to propagate through the waveguide between the optically coupled optical elements. The first wafer and the second wafer are optically coupled, for example, by optical elements on the first wafer being optically coupled to optical elements on the second wafer. As will be understood by one skilled in the art, optical as used herein refers to at least one of ultraviolet, visible, mid-infrared, infrared C-band, or infrared.

[0038] While a wafer as referred to herein may be, for example, a single layer of the same homogeneous material, in other embodiments, it is contemplated that a wafer may instead include one or more layers or portions that are each deposited or formed independently of one another (e.g., one after the other during a manufacturing process to form a stack of sublayers that together can be considered a wafer). A wafer may have portions of different materials, for example, due to manufacturing. In some embodiments, at least one of the optical amplifier or the electro-optically tunable optical filter comprises InGaAsP. In some embodiments, at least one of the electro-optically tunable optical filter and the optical amplifier comprises a first semiconductor material, or the thermally tunable optical filter comprises a second material. In some embodiments, at least one of the second material or third material described herein comprises at least one of a semiconductor, a dielectric, or a polymer. In various embodiments, at least one of the first semiconductor material, second material, or third material described herein includes at least one of Si, InP, gallium arsenide (GaAs), gallium antimony (GaSb), gallium nitride (GaN), indium gallium arsenide (InGaAs), indium aluminum arsenide (InAlAs), indium aluminum gallium arsenide (InAlGaAs), AlGaAs, InGaAsP, SiN, silicon oxide (SiO), tantalum pentoxide (TaO or tantala), aluminum oxide (AlO or alumina), aluminum nitride (AlN), or LiNbO. In further embodiments, other materials are also contemplated.

[0039] It will be understood that any feature described in connection with any one of the embodiments may be used alone or in combination with the other features described, and in combination with one or more other features of any of the embodiments, or in any other combination of any of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the appended claims.

Claims

1. a first wafer of a first semiconductor material supporting an optical amplifier and an electro-optically tunable optical filter; a second wafer of a second material different from the first semiconductor material supporting a thermally tunable optical filter; an optical cavity including the optical amplifier, the electro-optically tunable optical filter, and the thermally tunable optical filter; , a tunable laser.

2. the first wafer abuts the second wafer; the first wafer is on the second wafer; the first wafer supports the second wafer; or the second wafer supports the first wafer; 10. The tunable laser of claim 1, wherein the at least one of:

3. the electro-optically tunable optical filter; or the thermally tunable optical filter; 3. The tunable laser of claim 1, wherein at least one of said first and second lasers comprises a tunable resonator.

4. the electro-optically tunable optical filter; or the thermally tunable optical filter; 10. A tunable laser according to any preceding claim, wherein at least one of the first and second lasers comprises an interferometer.

5. the electro-optically tunable optical filter; or the thermally tunable optical filter; 10. A tunable laser according to any preceding claim, wherein at least one of the first and second lasers comprises an interferometer and a tunable resonator.

6. a scanning speed of the electro-optically tunable optical filter is at least 1000 times faster than a scanning speed of the thermally tunable optical filter; 10. A tunable laser according to any of the preceding claims, wherein the wavelength tuning range of the thermally tunable optical filter is ten times larger than the wavelength tuning range of the electro-optically tunable optical filter.

7. 10. A tunable laser according to any of the preceding claims, wherein the free spectral range of the electro-optically tunable optical filter is different from the free spectral range of the thermally tunable optical filter.

8. the first semiconductor material comprises indium phosphide; or the second material comprises silicon; 10. A tunable laser according to any one of the preceding claims, wherein at least one of

9. 10. A tunable laser according to any of the preceding claims, wherein the optical cavity is a linear optical cavity.

10. the first wafer or the second wafer is a substrate for a photonic integrated circuit; or 10. A tunable laser according to any preceding claim, wherein the first wafer and the second wafer are supported by a substrate for a photonic integrated circuit.

11. the electro-optically tunable optical filter and the optical amplifier comprise the first semiconductor material; or the thermally tunable optical filter comprises the second material.

10. A tunable laser according to any one of the preceding claims, wherein at least one of

12. A photonic integrated circuit comprising a tunable laser according to any of the preceding claims.

13. A device comprising the photonic integrated circuit of claim 12.

14. modulating the power of the output of the tunable laser; or Modulation of the peak wavelength of said output 14. The device of claim 13, comprising a controller configured for at least one of:

15. A method for manufacturing a tunable laser according to any one of claims 1 to 11, comprising the steps of: providing the first wafer of the first semiconductor material supporting the optical amplifier and the electro-optically tunable optical filter; providing the second wafer of the second material supporting the thermally tunable optical filter; optically connecting the first wafer to the second wafer such that the optical cavity of the tunable laser comprises the optical amplifier, the electro-optically tunable optical filter, and the thermally tunable optical filter; A method comprising:

16. A method for manufacturing a tunable laser according to any one of claims 1 to 11, comprising the steps of: providing the first wafer of the first semiconductor material; providing the second wafer of the second material; mechanically connecting the first wafer to the second wafer; forming the electro-optically tunable optical filter and the optical amplifier supported by the first wafer and the thermally tunable optical filter supported by the second wafer, such that an optical cavity of the tunable laser comprises the optical amplifier, the electro-optically tunable optical filter, and the thermally tunable optical filter; A method comprising:

17. 17. A method for manufacturing a photonic integrated circuit, comprising the method of claim 15 or 16.

18. A method for manufacturing a device, comprising the method according to any one of claims 15 to 17.

19. modulating the power of the output of the tunable laser; or Modulation of the peak wavelength of said output 20. The method of claim 18, comprising providing a controller configured for at least one of:

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